Conventional rotary kilns utilized for pyro-processing cement, lime, and other minerals, are commonly lined with refractories or bricks that protect the shells of rotary kilns against heat and abrasion. Generally, tapered bricks are placed in a ring manner along the circumference of the steel shell of the kiln. In addition to protecting the steel shell, the refractory bricks reduce the heat loss through the steel shell.
Unfortunately, conventional rotary kilns with present refractory lining designs are still heat inefficient, resulting in a prohibitively high fuel cost. For example, although the theoretical heat of formation of a Type I cement clinker is 420 kcal/kg, typical dry and wet process kilns consume far greater energy, approximately 1100 kcal/kg (38 % heat efficiency) and 1300 kcal/kg (32 % heat efficiency), respectively. Similarly, for lime kilns, typical heat efficiencies are in the range of about 40%. Such low heat efficiencies result from high radiative loss, in addition to heat loss resulting from surplus heat being dissipated in the stack gases, and the processed product itself.